Human groups, most of them we consider Germanic but also proto-Balto-Slavs and Iranic too, moved toward the Roman limes since centuries before Huns appeared in the Pontic steppe in the late IVth century. Probably not as a coherent groups or people, probably in various waves rather than one great migration, possibly as a mix of proto-Balto-Slavs, Iranians and Germanic elements that ended dominating culturally along the Danube.It wasn't the same case in the Rheinish limes and its hinterland, where a process of social stabilization trough Roman influence (trade and subsides, but as well development of farming techniques and social sophistication); even if movements due to the attraction of the limes probably happened (as it happened in the IInd century BCE with the Cimbric and Teutonic migrations)Climatic changes (especially on the coast) from the IInd century AD and crisis (up to the Third Century Crisis) in Rome led to a reconstruction of the Barbaricum, with migration and constitution of new coalitions and eventually peoples out of the melting-pot along the border made Barbarians more reliant on Roman products and neighbourhood (would it be only trough plunder) and middle to small scale migrations are attested outside and inside the Roman Empire; Barbarians being settled as defeated bands or as migrants in the provinces.

The Barbaricum outer periphery wasn't deserted, but the mix of social weariness, resources limitation, opportunities seems to have led to a less densely inhabited periphery, with maybe a less prosperous (or rather, less demonstrative in its display) society. So, when Huns eventually moved from the Pontic Steppe to settle in the Danubian basin, the "magnetic" pole, so to speak,of Barbarian peoples was already firmly set in the West and the South; Franks, Alamans, Tervingi for the most important already settling not as scattered groups or settled communities as laeti were; but as whole peoples leaving kin and land behind them (altough not too far).The coming of the Huns, on this regard, accelerated an existing trend that they don't really avoided for themselves. Even in the late IVth century, Huns were a mix of steppe peoples of various origin (Uralian, Iranic, Caucasian, proto-Turkic, mostly) and as they progressed West, incorporated Sarmatian and Germanic elements into their own people but as well as clients.Hegemonies as the Huns build over the Barbaricum are sometimes called "stateless empires" : their rule isn't built over a territorial control as such but a network of clientelisation and tributarisation.

Peoples confronted to Hunnic raids or attacks (or raids and attacks by their clients) would have the choice between outright submitting to their rule, hoping being spared the fight and negotiating a better treaty and a better part into the wealth amassed by the hegemony; risking a fight and the prospect having your men killed or enslaved (along with part of their families) and entering a more unequal or uneasy relationship; or not taking any chance and fleeing to a shelter.Huns didn't do much more on this principle that Greuthingi didn't do themselves in the IIIrd century (Maximian's Panygerics mention Goths killing off Burgundians and Alamans, fighting against virtually any of their neighbours); but they did so at a larger scale, due to possible tactical (greater mobility due to a more present cavalry; performing mounted archery) and political (rear alliance with Romans against Barbarians, which gave them access to rich subsides). Submitted people, while in an inferior position, were mixed with Huns to a certain degree, with Germanic or Sarmatian customs maybe influencing Huns more than the reverse (Attila, for instance, is a Gothic surname : maybe not the Hunnic king proper name, but one that was used to the point it's the only one we know).What submitted people had to provide were military forces, possibly resources such as cattle and grain as well.

Eventually, this hegemony was much more held together by the prestige, victories and redistributed wealth of Huns than outright terror : after Atilla's death, it quickly broke apart as formerly dominated people revolted in a bid to escape their hegemony or replace them.Enslavement itself must not have been this massive : the semi-nomadic nature of Huns is a bit contradictory with the need or reliance over a lot of slaves : Romans taken prisoners by Huns were rather ransomed back, or taken as hostages. Maybe some were "redistributed" to submitted peoples, but there was only this much capacity to hold a servile taskforce without it becoming unnecessary eaters; when swords and hands using them are always useful in a predatory leadership, when cattle can be killed and eaten, and with gold being an all-time favourite.

It's not even that certain that Huns were directly responsible of the flight of Hasdings, Silings and Suebi in 406/407 that broke the Rhenish limes. It depends on the historicity of a second Hunnic wave in Pannonia, trough the North, having led to Radagaisus's led people to move in Italy, and Vandals/Suebi groups to move west. Peter Heart argued in its favour, while acknowledging the absence of clear sources; Walter Goffart being cautious about affirming its existence for these reasons arguing that Huns could have replaced these peoples in Pannonia after they left the region.Arguably, Socrat the Scholastic does provides with a description of Burgundian fleeing Hunnic raids (in the late 400's at earliest) and converting to Nicean Christianism to be sheltered inside the empire : the point being that Huns might not have been the sole factor into the late IVth and early Vth century migrations it was taken for; although possibly decisive.

Huns, eventually, were as much drawn to the Roman limes than other Barbarians for similar reasons : when moving from the Pontic Steppe to the Pannonian plain, they mostly dealt with Barbarians along the Danube and the Rhine, and Hunnic presence North of Carpathian Mountains is barely evidenced. It's probably more a testimony to the mobility and projection capacity of Huns than a real dominance, even less control, from Danube "up to the islands in the Ocean" that Priscus describe, even if prestigious display shouldn't be dismissed, but we'd be more considering a broad influence there.

Overall, the relative impoverishment of the Barbaricum, and its relative depopulation in the Vth probably owes more to the successive crisis of the Roman Empire, its collapse being the last nail in the coffin that cut down a source of wealth, supplies and stabilization in western Germania and Scandinavia; than it owes to Huns, whom rule was more of a symptom of the general situation (if an influential one) than its overreaching cause.

- De les Goths aux Huns, le Nord de la Mer Noire au Bas Empire et à l'époque des grandes migrations; Mark Scukin, Michel Kazanski, Oleg Sharov; 2006

- Barbarian Tides; Walter Goffart; 2006

- The Fall of the Roman Empire; Peter Heather; 2005

- Les Vandales et l'Empire Romain; Yves Modéran; 2014